Vehicles operating in an autonomous mode (e.g., driverless) can relieve the driver from some driving-related responsibilities. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers.
Motion planning and control are critical operations in autonomous driving. A vehicle operating in an autonomous mode may encounter other autonomous driving vehicles. Accordingly, each autonomous driving vehicle may require planning and control based on potential driving maneuvers performed by another autonomous driving vehicle. For example, human motorists (e.g. drivers, cyclists, pedestrians, etc.) may communicate using various social interactions (e.g. hand signals, car horns, etc.). With autonomous driving vehicles, however, a driver may be a passive participant in driving-related responsibilities, and therefore, not active during vehicle operation. Moreover, because social interactions are not standardized, an autonomous driving vehicle attempting to interpret social interactions of other motorists by may be problematic. Accordingly, there is a need for a reliable communication system that may be used by autonomous driving vehicles.